XnConvert provides an action called “Replace color”, but you can't set the selected color to transparent.

Thanks for the quick reply!

I've played around with the Replace color but, like you said, I couldn't set it to transparent.

This person on Reddit assured me a while back that he was using XnConvert to achieve this result. Unfortunately, he hasn't been active in a while. Can you confirm than none of your software can achieve what I'm looking for?